A conductive member called a bus bar, which is a metal disposed as a power transmission line and the like, has conventionally been used in power plants, electric systems of transportation machines such as a vehicle, home electric appliances, and the like. The bus bar is in an elongated flat plate shape or in a long and thin rod shape, and due to a large surface area thereof, it has high heat dissipation and superior conductivity for allowing a large current to be flowed therein.
In addition to the heat dissipation and the conductivity, weight saving and cost reduction are also sought after in the above-described bus bar. To meet such a demand, for example, there has been proposed a compound electrode combining aluminum, which is lightweight and low-cost, with copper, which has high electrical conductivity. Among methods for joining two metals in this compound electrode, there are welding, a thermal spraying method, and a cold spraying method. The thermal spraying method is a method of forming a film by spraying a thermal spraying material, which is heated to a molten or nearly-molten state, onto a substrate.
The cold spraying method is a method of forming a film on a surface of the substrate by spraying powder of a material to be the film together with an inert gas, which is below a melting point or a softening point, from a convergent-divergent (Laval) nozzle. The material to be the film, which is in a solid state, is collided with the substrate (see, for example, Patent Document 1). In the cold spraying method, compared to the welding and the thermal spraying method, an influence of thermal stress is mitigated because a temperature used is low, no phase transformation occurs, and oxidization can be inhibited. Therefore, it is possible to obtain a metal film in which a decrease of electrical conductivity is restrained. In particular, in the case where both the substrate and the material to be the film are metal, plastic deformation occurs between the powder and the substrate by the powder to be the film colliding with the substrate, whereby an anchor effect can be obtained. Furthermore, in an area where the plastic deformation occurs, respective oxide films are destroyed when the powder collides with the substrate, and a metallic bond is formed between newly-formed surfaces, whereby an effect of obtaining a laminate having a high adhesive strength is also expected.